The actor and his abs appear in Monday's series premiere of Running Wild with Bear Grylls to do crazy, omg-stunts with the nature-surviving TV host.

"We reached out to him and he kindly said he was a fan of the show and that he was in 120 percent," Bear told People magazine about Zac being on board. "He asked for the biggest, baddest adventure and it was an honor to oblige."

Bear and Zac explored an area of the Catskills Mountains where special forces used to train back in the 1800s. To give Zac a reason to want to climb off a cliff with him, Bear threw their backpacks into the water below. We can't even...

"I can't believe how high this is," Zac says before they leap off. "I like to think he got to use his muscles to their max through the adventure," Bear told the mag.

Zac is the first of several celebs to go on a crazy adventure trip with Bear. Ben Stiller, Channing Tatum and NFLer Deion Sanders are also traveling to remote locations in hopes of...surviving.

#ZacEfron is hard at work filming #WeAreYouFriends, but he wants to THANK YOU for your support of his #MakeAWish raffle with an exclusive LIVE TWITTER CHAT from set! He'll hop online sometime TODAY between 7pm and 8pm PT for a 15 minute Q&A. Submit questions using #ZacsFirstCar and WATCH LIVE here: http://bit.ly/zacsfirstcar - #TeamZE #wayf

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